Lithium enrichment in the Galaxy: A study using the GALAH and Gaia surveys

2019 ◽  
Vol 14 (S353) ◽  
pp. 16-18
Author(s):  
Deepak ◽  
Bacham E. Reddy
Keyword(s):  
Mass Loss ◽  
Large Sample ◽  
Giant Stars ◽  
The Galaxy ◽  
Low Mass ◽  
Promising Source ◽  
Lithium Enrichment

AbstractHere, we explore the enrichment of Lithium in the Galaxy using a large sample of stars common among large spectroscopic surveys such as the GALAH and astrometric survey by the Gaia satellite. For this study we used about 60,000 low mass (M⩽ 2M⊙) dwarfs from the GALAH survey. Further, we discuss Li enrichment among giant stars based on a sample of 52,000 low mass giants, of which 335 are Li-rich with A(Li) ⩾ 1.80 ± 0.14 dex, culled from the GALAH survey. These low mass giants appears to be one of the promising source of Li enrichment in the Galaxy as their atmospheric Li can be added to the ISM through mass loss.

scholarly journals Lithium in Giant Stars

2000 ◽  
Vol 198 ◽  
pp. 310-319 ◽  
Author(s):  
Ramiro de la Reza
Keyword(s):  
Mass Loss ◽  
Chemical Evolution ◽  
Light Elements ◽  
Evolutionary Mechanisms ◽  
Set Constraints ◽  
Giant Stars ◽  
Mass Losses ◽  
The Galaxy ◽  
Lithium Enrichment ◽  
State Of Art

Lithium continues to be a surprising element and more than ever the study of its creation, destruction and distribution is giving us tools to understand, not only the chemical evolution of this element, but also the nature of mass loss of evolved giants and nucleosynthesis of other elements in cases of very low-metal giants. It also helps to set constraints for cosmological models. The presence of very strong lithium lines in some giant stars of different spectral types and stages of evolution has been considered up to the end of the nineties as a puzzle. To solve this problem, non standard evolutionary mechanisms must be invoked. We review here all the mechanisms presented in the literature and which are divided into internal and external processes of lithium enrichment. We will also discuss the observational tests which are being performed in order to discard (or not) some of them. In any case, the more realistic values of the lithium abundances in giants are, as we will see, the main test of these proposed scenarios. Because of this importance we discuss here the state of art of the Non-LTE determinations of lithium abundances in strong lithium giants. Evolved giants, with lithium abundances larger than that of the interstellar medium and with their important mass losses can be considered the most realistic sources of lithium in the Galaxy. We believe that a complete physical picture of this problem will give a powerful tool to understand the chemical evolution of a large part of all light elements.

Lithium Enrichment–Mass-Loss Connection in K Giant Stars

1996 ◽  
Vol 456 (2) ◽  
Author(s):  
R. de la Reza, ◽  
N. A. Drake, ◽  
L. da Silva
Keyword(s):  
Mass Loss ◽  
Giant Stars ◽  
Lithium Enrichment

scholarly journals Emerge: Empirical predictions of galaxy merger rates since z ∼ 6

2020 ◽  
Author(s):  
Joseph A O’Leary ◽  
Benjamin P Moster ◽  
Thorsten Naab ◽  
Rachel S Somerville
Keyword(s):  
Galaxy Formation ◽  
Power Law ◽  
Stellar Mass ◽  
Direct Result ◽  
Mass Relation ◽  
Massive Galaxies ◽  
The Galaxy ◽  
Major Merger ◽  
Low Mass ◽  
Merger Rate

Abstract We explore the galaxy-galaxy merger rate with the empirical model for galaxy formation, emerge. On average, we find that between 2 per cent and 20 per cent of massive galaxies (log10(m*/M⊙) ≥ 10.3) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power-law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies log10(m*/M⊙) ≳ 11.0. For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as 90 per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation timescales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation timescale that decreases linearly with redshift as Tobs = −0.36(1 + z) + 2.39 [Gyr], assuming all observed pairs merge by z = 0.

scholarly journals Cosmological simulations of low-mass galaxies: some potential issues

2010 ◽  
Vol 6 (S270) ◽  
pp. 503-506
Author(s):  
Pedro Colín ◽  
Vladimir Avila-Reese ◽  
Octavio Valenzuela
Keyword(s):  
Star Formation ◽  
Adaptive Mesh Refinement ◽  
Mass Fraction ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Mesh Refinement ◽  
Adaptive Mesh ◽  
Stellar Mass ◽  
The Galaxy ◽  
Low Mass

AbstractCosmological Adaptive Mesh Refinement simulations are used to study the specific star formation rate (sSFR=SSF/Ms) history and the stellar mass fraction, fs=Ms/MT, of small galaxies, total masses MT between few × 1010 M⊙ to few ×1011 M⊙. Our results are compared with recent observational inferences that show the so-called “downsizing in sSFR” phenomenon: the less massive the galaxy, the higher on average is its sSFR, a trend seen at least since z ~ 1. The simulations are not able to reproduce this phenomenon, in particular the high inferred values of sSFR, as well as the low values of fs constrained from observations. The effects of resolution and sub-grid physics on the SFR and fs of galaxies are discussed.

scholarly journals The properties of early-type stars in the Magellanic Clouds

2008 ◽  
Vol 4 (S256) ◽  
pp. 325-336
Author(s):  
Christopher J. Evans
Keyword(s):  
Physical Properties ◽  
Mass Loss ◽  
Temperature Scale ◽  
Massive Stars ◽  
Magellanic Clouds ◽  
Early Type ◽  
The Past ◽  
The Galaxy ◽  
Stellar Temperature ◽  
Early Type Stars

AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

scholarly journals Footprints of triggering in large area surveys of the nearby ISM and YSOs

2006 ◽  
Vol 2 (S237) ◽  
pp. 124-127
Author(s):  
L. Viktor Tóth ◽  
Zoltán T. Kiss
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Large Area ◽  
Large Sample ◽  
Low Mass ◽  
Cold Core

AbstractOur goal is to evaluate the role of triggering effects on the star formation and early stellar evolution by presenting a statistically large sample of cloud and low-mass YSO data. We conducted large area surveys (ranging from 400 square-degree to 10800 square-degree) in optical, NIR and FIR. The distribution of the ISM and low-mass YSOs were surveyed. A relative excess was found statistically in the number of dense and cold core bearing clouds and low mass YSOs in the direction of the FIR loop shells indicating a possible excess in their formation.

Metallicity, pulsation and mass loss in globular cluster low-mass AGB stars

2009 ◽  
Author(s):  
Iain McDonald ◽  
Jacco Th. van Loon ◽  
Martha L. Boyer ◽  
Eric Stempels
Keyword(s):  
Mass Loss ◽  
Globular Cluster ◽  
Agb Stars ◽  
Low Mass

scholarly journals The Evolution of 3He, 4He and D in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 540-546 ◽  
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Present Model ◽  
Galactic Disk ◽  
The Sun ◽  
Mixing Process ◽  
Low Mass Stars ◽  
A Value ◽  
The Galaxy ◽  
Low Mass ◽  
Standing Problem

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

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